Single-cell mapping reveals several immune subsets associated with liver metastasis of pancreatic ductal adenocarcinoma

Background: Identifying a metastasis-correlated immune cell composition within the tumor microenvironment (TME) of pancreatic ductal adenocarcinoma (PDAC) will help to develop promising and innovative therapeutic strategies. However, the dynamics of immune cell lineages in the TME of advanced PDAC remains elusive.Methods: Twenty-six samples from 11 patients (including 11 primary tumor tissues, 10 blood, and 5 lymph nodes) with different stages were used to develop a multiscale immune profile. High-dimensional single cell analysis with mass cytometry was performed to search for metastasis-correlated immune changes in the microenvironment. The findings were further validated by published single-cell RNA sequencing (scRNAseq) data and multiplex fluorescent immunohistochemistry.Findings: High-dimensional single-cell profiling revealed that the three immune-relevant sites formed a distinct immune atlas. Interestingly, the PDAC microenvironment with the potential for metastatic spread to the liver was characterized by a decreased proportion of CD103+ PD-1+CD39+ T cells with cytotoxic and exhausted functional status and an increased proportion of CD73+ macrophages. Analysis of scRNA-seq data of PDAC further confirmed the identified subsets and revealed strong potential interactions via various ligand-receptor pairs between the identified T subsets and the macrophages. Moreover, stratified patients with different immune compositions correlated with clinical outcomes of PDAC.Conclusions: Our study uncovered metastasis-correlated immune changes, suggesting that ecosystem-based patient classification in PDAC will facilitate the identification of candidates likely to benefit from immunotherapy.